nostr:npub16kfshp0c20gqd9m8caqn27s0tgmju4ydqk940ehzg8rwxl7zcfus3ud3nq Nebula is basically entirely owned by a bunch of YouTube creators that were sick of YouTube.
From what I know it's not that "open". Currently it's more like a small "oligarchy" of high-quality content creators (among the founders there are the guys from Real Engineering, 3blue1brown, TL;DR News, Wendover productions etc.) that fully control the content, the business, the distribution platform and the app - and I guess also who can sign up as a creator, through a traditional contract.
It goes on a subscription-based model, but at $5/month in exchange for a good half of the content from high-quality YouTube creators in science and tech it's a quite honest deal. I'd also be ok to pay that money to YouTube, if only they allowed me to watch the same content on their platform without ads.